Plant cells have a variety of shapes that greatly affect their function. These shapes are achieved by precisely controlled cell wall expansion. The long term goal of the proposed research is to understand the molecular and genetic mechanisms underlying this process which is so intimately tied to plant form and function. The differentiation of trichomes (hairs) on the epidermis of the plant, Arabidopsis thaliana is being used as a model system to study plant cell morphogenesis. Arabidopsis trichomes are large, single cells with a stalk and generally three branches. Plants homozygous for the recessive stalkless (stl) mutation have trichomes with a greatly reduced stalk and only one or two branches. The wild-type STL locus has been cloned from arabidopsis, and DNA sequence that it encodes a member of the kinesin- like family of microtubule motor proteins. The goal of the proposed research is to determine the function of the STL gene, and define interactions between the stl mutation and other mutations which affect trichrome morphology. The specific goals are: (1) To complete the physical characterization of the STL locus. This includes determining the limits of the gene and sequencing the cDNA. (2) To determine the expression pattern of the STL gene and the subcellular location of the STL protein in wild type plants. (3) To examine the effect of altered expression of the STL gene by transformation of wild type plants and trichrome mutants with STL coding sequences under the control of heterologous promoters. (4)To define interactive and epistatic interactions between different mutations which affect trichome morphogenesis, specifically trichome branching. This includes the analysis of STL expression in the various trichome branch mutants. (5) To isolate and characterize genetic suppressors and ehancers of the stl mutation as a method of identifying other genes which affect trichome morphogenesis, and potentially interact with STL. The results of these experiments will lead to a better understanding of how trichomes attain their specific shape. Ultimately, a thorough understanding of the molecular and genetic control of trichome cell shape should lead to a detailed paradigm of plant cell morphogenesis and may provide insight into animal cell morphogenesis as well.